This invention relates to light emitting devices and methods of fabricating the same, and more particularly, to Light Emitting Diodes (LEDs) and methods of fabricating LEDs.
LEDs are widely known solid-state lighting elements that are capable of generating light upon application of voltage thereto. LEDs generally include a diode region having first and second opposing faces, and include therein an n-type layer, a p-type layer and a p-n junction. An anode contact ohmically contacts the p-type layer and a cathode contact ohmically contacts the n-type layer. The diode region may be epitaxially formed on a substrate, such as a sapphire, silicon, silicon carbide, gallium arsenide, gallium nitride, etc., growth substrate, but the completed device may not include a substrate. The diode region may be fabricated, for example, from silicon carbide, gallium nitride, gallium phosphide, aluminum nitride and/or gallium arsenide-based materials and/or from organic semiconductor-based materials. Finally, the light radiated by the LED may be in the visible or ultraviolet (UV) regions, and the LED may incorporate wavelength conversion material such as phosphor.
The diode region of many LEDs is fabricated from Group III Nitride layers. Moreover, the LED may include a mesa that includes a Group III Nitride mesa face and a mesa sidewall, on an underlying LED structure. As used herein, the term “Group III Nitride” refers to those semiconducting compounds formed between nitrogen and the elements in Group III of the periodic table, usually aluminum (Al), gallium (Ga), and/or indium (In). The term also refers to ternary and quaternary compounds such as AlGaN and AlInGaN. As is well understood by those in this art, the Group III elements can combine with nitrogen to form binary (e.g., GaN), ternary (e.g., AlGaN, AlInN), and quaternary (e.g., AlInGaN) compounds. These compounds all have empirical formulas in which one mole of nitrogen is combined with a total of one mole of the Group III elements. Accordingly, formulas such as AlxGa1-xN where 0≦x≦1 are often used to describe them. Moreover, the Group III Nitride compound may be doped p-type and/or n-type using, for example, p-type dopants such as magnesium and/or n-type dopants such as silicon. Finally, other elements may also be present in the Group III Nitride.
It is often desirable to texture a surface of a Group III Nitride layer in an LED, for example, to facilitate light extraction and/or for other purposes. A major advancement in texturing of a Group III Nitride surface is described in U.S. Pat. No. 8,357,923 to Edmond et al., entitled External Extraction Light Emitting Diode Based Upon Crystallographic Faceted Surfaces, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As described in the Abstract of U.S. Pat. No. 8,357,923: “A light emitting diode is disclosed that includes a support structure and a Group III nitride light emitting active structure mesa on the support structure. The mesa has its sidewalls along an indexed crystal plane of the Group III nitride. A method of forming the diode is also disclosed that includes the steps of removing a substrate from a Group III nitride light emitting structure that includes a sub-mount structure on the Group III nitride light emitting structure opposite the substrate, and thereafter etching the surface of the Group III nitride from which the substrate has been removed with an anisotropic etch to develop crystal facets on the surface in which the facets are along an index plane of the Group III nitride. The method can also include etching the light emitting structure with an anisotropic etch to form a mesa with edges along an index plane of the Group III nitride.” See the Abstract of U.S. Pat. No. 8,357,923.